Caroline Nicholls, HGCA research and knowledge transfer manager, says every sample sent in over the summer showed knock-down resistance (kdr), but, more worryingly, high levels of the kdr-RR resistant beetles were found in each sample.

“This is a cause for concern as this type of resistance is likely to cause control problems when using all pyrethroids applied at recommended field rates.”

The HGCA is now urging growers and agronomists who are experiencing control issues to send off cabbage stem flea beetle samples for analysis by Rothamsted Research, to help build a better picture of the scale of the problem.

“We found the best way to catch live beetles is to go out at night with a torch to find them. Once located, beetles can then be trapped using a jar,” explains Miss Nicholls.

Oilseed rape plants that have already emerged will be less vulnerable to damage, however CSFB will lay eggs at the base of the crop and, if conditions are mild, larvae may enter plants to feed from October to early April.

If more than 35 beetles are caught in yellow water traps or if two larvae/plants are found in late October and early November, then growers are advised to treat crops.